Aim. The present study was conducted to determine the optimal conditions for invertase production by Aspergillus niger ATCC 20611.Methods. Sucrose and the combination of yeast extract and NaNO3 were found to the most suitable carbon and nitrogen sources, respectively for invertase production by Aspergillus niger ATCC 20611.Results. The strain produced a high amount of extracellular invertase (3072 U/mL) in an optimal culture medium containing 10% (w/v) sucrose, 1% (w/v) yeast extract in combination with 1.5% (w/v) NaNO3, 1 mM (v/v) Ca+2 and 1% (v/v) Triton X-100 (pH 6.0) after 96 h of incubation at 30ºC and 200 rpm when inoculated with 6% (v/v) of the inoculums.Conclusion. Thermal characterisation suggested 50 ºC as the optimum temperature for enzyme activity. In this temperature, the enzyme was shown to be stable for 3 h. The optimal conditions as obtained can be potentially considered for large scale production of the enzyme.